OOTO Messages are getting stuck in the Categorizer

Have you ever experienced a situation where OOTO responses to external addresses fail to be delivered?
It's weird. I'm looking at one example today where in message tracker it says
"SMTP: Mail Submitted to Categorizer" - and that's as far as it goes.

Internally, OOTO works fine. But from the outside, external addresses get no response.

There are cases when e.g. an IT administrator wants to have full access and view into selected mailboxes on Exchange server, directly from his own email account in Outlook or Outlook Web Access. This proves useful when for example administrator want…